JP2006335887A - Fluorescent plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for eliminating an uneven part formed on a vacuum evaporation surface when forming a fluorescent substance layer by vacuum evaporation. <P>SOLUTION: The fluorescent substance layer, for example, a fluorescent plate 4 obtained by growing a columnar crystal of CsI has a face having a recessed part and/or a protruded part formed by splash (caused by flying out of the CsI in a solid state before being completely vaporized into a vacuum vessel, and attaching of the solid on the vacuum evaporation surface to form the uneven part). The surface of the CsI is flattened by arranging a glass plate 7 having good flatness on the fluorescent plate 4, and pushing in the crystal structure of the protruded part while breaking the crystal structure of the protruded part by pressurizing the upper part of the glass plate 7 and rotating the roller 8 in the arrow direction to flatten the surface of the CsI. In another embodiment, the surface of the CsI is flattened by moving a tool along the flat surface of the CsI to remove the protruded part, and filling the recessed part with a fluorescent substance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a medical radiation detection system, an industrial nondestructive inspection system, and the like using a fluorescent screen.

  FIG. 15 is a sectional view of an X-ray area sensor of a conventional medical radiation detection system. A photoelectric conversion element 112 arranged in a grid pattern on the optical sensor 111, an optical sensor protective layer 113, a columnar phosphor 114, an adhesive layer 115, a reflective layer 116, and a protective layer 117 are formed to form an X-ray. An area sensor is created.

  X-rays incident on the phosphor 114 are wavelength-converted from the X-rays to light such as visible light by the phosphor 114, and then the visible light is photoelectrically converted by the photoelectric conversion element 112 of the optical sensor 111 and converted into an electrical signal. . An X-ray digital image can be obtained by amplifying the signal and applying image processing.

  Currently, as means for forming the columnar phosphor 114 on the photosensor 111, a method of directly depositing the phosphor 114 on the photosensor 111 and a base 121 separate from the photosensor 111 as shown in FIG. There is a method in which the reflective layer 124 and the phosphor 125 are vapor-deposited and covered with the protective layer 128, and then attached to the optical sensor 111 via the adhesive 140 using a roller or the like.

  Comparing the two, the former has the advantage of reducing the number of manufacturing steps and the cost, and the latter has the advantage that it is not affected by the yield at the time of phosphor deposition formation. Further, CsI (cesium iodide) is mainly used as the phosphor for the X-ray area sensor from the viewpoint of light emission amount and resolution, and the method of forming on the phosphor substrate is often by vacuum deposition. .

  Hereinafter, a method for forming a phosphor on an optical sensor by bonding will be described. As the material of the phosphor substrate 121 on which the phosphor is formed, an amorphous carbon (a-C) with little X-ray absorption, an inexpensive glass substrate, or an aluminum plate or the like is used as a material that also serves as the reflective layer 124 at the same time. The

  First, as shown in FIG. 16, a protective film 123 is formed on the phosphor substrate 121, and a reflective layer 124 is formed thereon by vapor deposition. Since the protective film 123 isolates the phosphor substrate 121 and the reflective layer 124, the reflective layer 124 reflects the phosphor light emitted in the opposite direction to the photosensor so that the photosensor can detect it efficiently. Formed for. Polyparaxylylene resin or the like has been used as a material for the protective film 123, and a metal or a metal compound material such as Al or Ag having high reflectivity is used as a material for the reflective layer 124. This is done.

  Next, a protective film 122 such as polyparaxylylene resin is formed so as to cover the reflective layer 124, and a phosphor 125 is formed thereon. CsI or the like is used as the material of the phosphor 125. The case of forming by vacuum deposition using CsI will be described below. The protective film 122 is formed in order to prevent mutual corrosion caused by direct contact between the reflective film 124 of the metal or metal compound material and the phosphor layer.

  The phosphor substrate 121 on which the protective film 122 is formed is set in a vacuum chamber, and CsI (Na +) or CsI (Tl +), which is an evaporation material, is placed in the port. The pressure in the vacuum chamber is pulled to 0.1 to 1.0 [Pa], the phosphor substrate 121 on which the reflective layer 102 is formed is heated to a high temperature (about 100 to 180 ° C.), and a current is passed through the port for heating. Then, CsI is vaporized and CsI columnar crystals are formed on the phosphor substrate 121 on which the reflective layer 124 is formed.

  Further, a protective layer 128 for protecting from mechanical stress and moisture is formed on the phosphor 125 or on the entire circumference of these layers. Since the protective layer 128 enters between the fluorescent material and the optical sensor when the fluorescent plate and the sensor are bonded together, the protective layer 128 must be formed of a material having a high light transmittance and thin.

  When the transmittance is low, the light emitted from the phosphor 125 is absorbed by the protective layer 128, and the sensitivity of the photosensor is lowered. Further, when the protective layer 128 is thick, the distance between the phosphor and the photosensor is increased, and the light from the phosphor 125 is scattered, so that the resolution of the photosensor is lowered. Furthermore, when CsI is used for the phosphor 125, since CsI has deliquescence, a material with low moisture permeability must be used so that it can be protected from moisture. The polyparaxylylene resin is a material that satisfies these conditions.

  Finally, the surface of the phosphor 125 is bonded to the sensor substrate 111 with the adhesive 140, and the sensor outer periphery is protected with the sealant 129 for moisture prevention.

As another conventional example, Patent Document 1 can be cited.
JP2003-066196

  By the way, in the conventional example shown above, when the phosphor layer is formed by vapor deposition of CsI, before CsI is completely vaporized (in a solidified state), it jumps out into the vacuum chamber, and the solid matter is a protective film. 104 may adhere to the deposition surface. This is called splash.

  As shown in FIG. 17, the splashed CsI appears as a convex portion 5 having a size (diameter) of about several tens to several hundreds of μm and a height of about ten to several hundreds of μm. . Further, at the same time as the convex portion 5, a concave portion 6 having a gap width of several to several tens of μm and a depth of several tens to several hundred μm is also generated in the periphery thereof. In addition, the splash is generated due to the foreign matter adhering to the phosphor substrate 121, the reflective layer 124 and the protective films 122 and 123 before the vapor deposition, or the foreign matter adhering to the vapor deposition surface during the vapor deposition or immediately after the vapor deposition.

  An effective method for eliminating the unevenness of the CsI surface due to these causes has not been considered at present. Further, if the thickness of the phosphor 125 is increased, the vapor deposition time is increased accordingly, so that the phosphor 125 is likely to be generated, and the generation rate is increased even if the vapor deposition area is increased.

  As shown in FIG. 17, when the phosphor 125 made of CsI is formed by vacuum deposition, irregularities due to splash or foreign matter appear, and the convex portion 5 has a height of several tens to several hundreds of μm as described above. Since the protective layer is as thin as several μm to several tens of μm, it appears in the same size as the unevenness before the formation of the protective layer 128.

  In addition, as shown in FIG. 17, in the concave portion 6 around the convex portion 5, there is a gap of several μm to several tens of μm, so that the protective layer 128 is not formed or is thinner than other portions. There is also. The gap is not filled unless a protective layer having a gap distance is formed. However, when the protective layer has a thickness of several tens of μm, there is a problem that the resolution deteriorates.

  By bonding the fluorescent plate in which the protective layer 123, the reflective layer 124, the protective layer 122, the phosphor 125, and the protective layer 128 are formed on the phosphor substrate 121 as described above to an optical sensor via an adhesive, It becomes an X-ray sensor.

  When the fluorescent plate is bonded to the optical sensor 111 via the adhesive 140, the adhesive 140 is formed between the phosphor 125 and the optical sensor 121, similarly to the protective layer 128. Therefore, the light transmittance and film thickness are important.

  As a general bonding of the phosphor 125, the adhesive 140 is applied on the optical sensor 111, the phosphor 125 is overlaid thereon, and bonding is performed while pressing with a roller. At that time, the thickness of the adhesive 140 is controlled by the load / moving speed of the roller and the viscosity of the adhesive 140.

  As described above, when phosphor (especially CsI) is formed on a phosphor substrate by vapor deposition, irregularities of several tens to several hundreds of μm are generated due to splash or foreign matter. Due to these irregularities, the following problems occur when the fluorescent plate and the optical sensor are bonded together.

(1) Destruction of the optical sensor As shown in FIG. 16, the optical sensor 111 is covered and protected by the optical sensor protective layer 113, but the optical sensor 111 is damaged by the protrusion on the bonding surface of the phosphor 125. It will destroy. The optical sensor 111 is a collection of photoelectric conversion elements 112 arranged in a lattice pattern, but the number of photoelectric conversion elements 112 that are destroyed increases depending on the size or number of protrusions. Further, when the wiring portion connecting the photoelectric conversion elements 112 is broken, it leads to the destruction of all the columns of the photoelectric conversion elements 112.

(2) Destruction of the protective layer If the surface of the fluorescent plate is uneven, the load of the roller is concentrated on the convex portion at the time of bonding, and the convex phosphor 125 and the protective layer 128 are crushed. Therefore, cracks (cracks) occur in the protective layer 128.

  Further, in the concave portion, there is a portion where the protective layer 128 is not covered when the protective layer is formed, and the phosphor 125 is exposed, and when the temperature and humidity durability test is performed, the crack and the concave portion not covered with the protective layer 128 In some cases, moisture (moisture) enters the phosphor 125 and the phosphor 125 may be destroyed. In particular, when the phosphor 125 is CsI, it is deliquescent.

(3) Decrease in resolution In the bonding of the fluorescent plate 125 and the optical sensor 111, the film thickness of the adhesive 140 after formation is important, and 20 μm or less is desirable for obtaining high resolution. However, the concavo-convex portions on the surface of the fluorescent plate 125 are often several tens to hundreds of tens of μm. The thickness must be increased to a thickness of 20 μm or more (a thickness of a few tens of μm). As a result, the distance between the phosphor 125 and the optical sensor 111 becomes large and the resolution decreases.

(4) Intrusion of bubbles The unevenness of the fluorescent plate 125 may not only destroy the protective layer 113 and the optical sensor 111 but also embrace bubbles during bonding. If there are innumerable convex portions on the surface of the fluorescent plate 125, the load of the rollers is concentrated on the convex portions, the roller load is not applied to the adhesive 115, and the adhesive 140 is difficult to spread.

  Moreover, even when there are few convex parts, the location where a load is not applied will generate | occur | produce around a convex part, and it will become impossible to push away a bubble. For this reason, bubbles remain between the fluorescent plate 109 and the optical sensor 111, so that the light emitted from the phosphor 125 is diffusely reflected to lower the resolution.

(5) Image abnormality The medical radiation detection system uses X-rays as described above.

  Although the explanation about the generation mechanism of X-rays is omitted, there are soft X-rays and hard X-rays in X-rays, and the density in the human body, for example, the absorption rate of X-rays differs between the bone part and the boneless part. The X-ray quality is changed according to the site of the affected area.

  The quality of X-rays differs depending on the tube voltage for driving the generator. For example, soft X-rays are generated at a low tube voltage such as 50 kV, and hard X-rays are generated at a high tube voltage such as 140 kV.

  By the way, the sensors used in the radiation detection system are formed with millions of pixels, and each of them has different characteristics. It is not suitable as an image to be used. For this reason, the system uses a unique correction method to perform calibration so that the characteristics of each pixel match. At the time of photographing, a diagnostic image is generated using the calibration data for raw sensor output.

  The calibration is performed using each pixel output when photographing at a standard tube voltage, for example, 80 kV. However, as described above, the tube voltage for imaging is not always constant because it is performed at a tube voltage suitable for the body part. The system is required to output an image with no sense of incongruity with the same calibration data even if the tube voltage for photographing is different.

  When the tube voltage for calibration and the tube voltage for shooting are different, there may be a feeling of strangeness in the image. This is unevenness of the phosphor layer that converts X-rays into visible light. In particular, the difference in density of the phosphors is affected by the quality of the radiation, causing image abnormalities in part and causing misdiagnosis.

  In the conventional example, in the splash portion of CsI, the crystal partially grows abnormally and uneven portions are generated, and unevenness in the thickness (height) direction means that there is a difference in phosphor density at that portion. The greater the splash, the more abnormal the image will be when shooting with a different tube voltage.

  As described above, the unevenness of the phosphor causes problems such as the above (1) to (5), so that flattening and uniform density are important issues.

  In order to solve the above-described problems, the present invention is characterized in that, in the process of manufacturing a fluorescent plate, the convex portion of the portion where the convex portion is formed is removed and the concave portion is filled with a phosphor.

  As described above, in the present invention, by removing the projections of the splash and filling the recesses around the splash with the fluorescent material, various problems caused by the splash generated during the deposition of CsI are solved, and as a sensor in a medical radiation system, We were able to achieve stable performance and provide a highly reliable sensor.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  First, the basic concept of the present invention will be described. The above-mentioned problem is solved by removing the protrusions on the surface of the fluorescent plate before bonding and filling the recesses with phosphor.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an X-ray inspection system using the X-ray inspection apparatus of the present invention. In general, an X-ray inspection system includes an X-ray room for X-ray imaging, a control room for the X-ray imaging, and a doctor room for diagnosing the captured image. In FIG. 1, 800 is an X-ray, 801 is an X-ray tube which is an X-ray generation unit, 802 is an X-ray image sensor, 803 drives an image sensor 802, and acquires an image taken by the image sensor 802. An image processor for transmitting information to an external output device, 804 a display for confirming an image at the time of shooting, 805 an image transmission system, 806 a film processor and a laser system for outputting an image to a film, and 807 A display 808 for diagnosis is a film output from 806.

  The present invention relates to a fluorescent plate that is disposed inside an image sensor 802 and converts X-rays into visible light.

  In particular, since it is a splash countermeasure made of CsI, it can be applied to all fluorescent plates of a radiation detection system or an industrial inspection system using vapor deposition CsI as a phosphor, and CsI is directly applied to a fluorescent plate made of CsI shown in the conventional example as a sensor. Needless to say, it can be applied to either a direct deposition type or a type to be attached to a sensor.

  First, the removal of the convex portion on the CsI surface and the filling of the phosphor into the concave portion will be described.

  FIG. 2 is a schematic cross-sectional view of a type in which CsI is directly deposited on the sensor.

  In the figure, 1 is a sensor substrate, 2 is a photoelectric conversion portion, 3 is a protective film, 4 is a crystal-shaped fluorescent plate formed of CsI, 5 is a projection of the splash, and 6 is a recess around the splash.

  FIG. 3 is a schematic cross-sectional view of an indirect type in which CsI is vapor-deposited on a support substrate and the fluorescent plate is bonded to a sensor substrate. In FIG. 3, 11 is a support substrate, 12 is an insulating film, 13 is a reflective film, 14 is a protective film, 15 is a fluorescent phosphor plate made of CsI, 16 is a convex portion of splash, and 17 is a concave portion around the splash. is there.

  The present invention relates to a measure against splash on the fluorescent screen, and is common to both the direct type shown in FIG. 2 and the indirect type shown in FIG. The direct type sensor shown in 2 is used. It goes without saying that the effects of the invention are the same for joint types.

  The first embodiment of the present invention will be described below. FIG. 4 is an enlarged cross-sectional view of a splash portion of the fluorescent plate 4 of FIG. As in FIG. 2, reference numeral 5 denotes a splash convex portion, and reference numeral 6 denotes a concave portion around the splash. Splash grows abnormally due to foreign matter or the like during the crystal growth of CsI. As shown in FIG. 4, splash is generated in the middle of crystal growth. 5 and 6 show the process of crushing the projection 5 of the splash. 5 and 6, 7 is a plate made of glass or the like that is harder than CsI and has good flatness, and 8 is a roller. First, the glass plate 7 is disposed on the fluorescent plate 4, and the roller 8 is rolled in the arrow direction while pressing the upper portion of the glass plate 7. Thereby, the convex part of the columnar crystal of CsI is pushed in while breaking the crystal structure by the pressure from above. The uppermost surface of the convex portion that has been pushed in coincides with the portion without splash, and the CsI surface can be flattened.

  FIG. 7 is an enlarged cross-sectional view of the splash portion from which the convex portion is eliminated according to FIG.

  In FIG. 7, the shaded portion 21 is a crushed splash portion.

  FIG. 8 is an enlarged cross-sectional view of a state in which the recess 6 around the splash is filled with a fluorescent material.

  In FIG. 8, 6 is a recess around the splash, and 9 is a filled fluorescent material. Here, the fluorescent material 9 is the same compound as CsI: Tl constituting the phosphor layer, and a granular material of several microns to several tens of microns is suitable for facilitating filling of the narrow concave portion 6. In addition, the compound of CsI and Tl can be produced under the same deposition conditions as those for producing the phosphor film of CsI.

  Filling the recess 6 with the compound of CsI: Tl is possible by sprinkling the compound around the recess 6 and pushing it in with a brush or the like. It is also possible to vibrate the granular compound with a vibration generator and fill the recess with the compound. Excess CsI: Tl compound remaining on the phosphor layer surface after filling can be removed by wiping air or the like.

  In addition to CsI: Tl, the fluorescent substance 7 is a substance that emits light by radiation such as X-rays (meaning electromagnetic waves coming from the fluorescent plate, including α, β, γ rays, etc. in addition to X-rays). Gd 2 O 2 S : Tb, Y2O2S: Tb, (Gd, Y) 2O2S: Tb, La2O2S: Tb, (Gd, Y) 2O2S: Tb: Tm, GdTaO4: Tb, Gd2O3, Ta2O5, B2O3: Tb, CaWO4, BaO4, Pb, LaO4 : Tm, LaOBr: Tb, HfO2: Ti, HfP2O7: Cu, CdWO4, YTaO4, YTaO4: Tm, YTaO4: Nb, ZnS: Ag, BaFCl: A phosphor exhibiting high-efficiency instantaneous light emission by X-ray excitation. Any of them can be used.

  Next, a second embodiment of the present invention will be described. The difference from the first embodiment is in how to remove the projections of the splash.

  The tip of the splash of CsI is a lump of sharp protrusions. As shown in FIG. 9, when the protrusions are touched with the adhesive tape or the like at the time of attachment, the protrusions 22 are held on the adhesive material side. As a result, only the splash protrusions It is possible to get rid of. At that time, the cut portion of the splash portion is on the inner side of the flat surface, and is near the depth of the concave portion or on the flat surface side. That is, it is cut at the weakest part by the shape of the splash, and the shape after cutting becomes a hole-shaped recess as shown in FIG.

  FIG. 10 is a schematic view of a state in which the concave portion is filled with the fluorescent material 9. The filling method can be performed in the same manner as in Example 1, and the description thereof is omitted here.

  In the first embodiment, the columnar crystal of CsI is broken by crushing the convex portion. However, in the second embodiment, the columnar crystal structure of the remaining portion of the splash site is not changed. Highly efficient propagation of light, which is a feature, is possible.

  Next, a third embodiment of the present invention will be described. The difference from the first and second embodiments is in how to remove the projections of the splash.

  FIG. 11 is a diagram showing a method of removing only convex portions from the flat surface along the flat surface of CsI. A tool 24 made of a metal or plastic having a certain degree of hardness and good linearity for removal is moved sideways along the flat surface of CsI, and only the convex portion 23 is removed.

  In the first embodiment, the CsI columnar crystals were broken by crushing the protrusions. In the second embodiment, the thickness of the columnar crystal in the splash portion is thinner than the thickness of the columnar crystal in the flat portion, but in the third embodiment, since only the convex portion can be removed from the flat surface, The thickness of the columnar crystal at the splash site after removing the convex portion is equal to the thickness of the flat site, and the difference in the degree of light propagation is the smallest.

  FIG. 12 is a cross-sectional view of a state in which the concave portion is filled with a fluorescent material. The filling method can be performed in the same manner as in Example 1, and the description thereof is omitted here.

  In Examples 2 and 3, it goes without saying that the same effect can be obtained even if the fluorescent material is a fluorescent substance other than CsI: Tl shown in Example 1.

  In any of the embodiments, since the phosphor layer made of CsI has the property of being deliquescent by moisture, a moisture-proof protective film is applied so as to cover the phosphor layer after filling the recess with the phosphor material. It is necessary. As with the conventional example, the moisture-proof protective film can deposit polyparaxylylene. However, depending on the deposition conditions, the characteristics of the filled fluorescent material may change. It is most desirable to form a film with.

  FIG. 13 shows a sensor configuration when the third embodiment is applied to a direct type in which CsI is directly deposited on the sensor.

  In the figure, 31 is a hot melt film which is a moisture-proof protective film made of a thermoplastic resin, 32 is a reflective film such as metal, and 33 is an organic film such as PET as a support. The same reference numerals as those in FIG.

  FIG. 14 shows a sensor configuration in the case where the third embodiment is applied to a bonded type of a fluorescent plate and a sensor. In the figure, 18 is a moisture-proof protective film, 19 is a peripheral sealing resin, and 40 is a hot melt which is a thermoplastic resin. The description of the same reference numerals as those in FIG.

1 is a schematic diagram of a medical radiography system. The schematic sectional drawing of the direct vapor deposition type of fluorescent substance. The schematic sectional drawing of the indirect bonding type of fluorescent substance. The expanded sectional view of the uneven | corrugated | grooved part of columnar shape fluorescent substance. The figure which shows the flat process of the fluorescent substance convex part of this invention. The flat process of the fluorescent substance convex part of this invention is shown. The expanded sectional view after flattening the fluorescent substance convex part of this invention. The expanded sectional view after the fluorescent substance filling of this invention. The expanded sectional view which shows the 2nd Example of this invention. The expanded sectional view after fluorescent substance filling which shows the 2nd Example of this invention. The expanded sectional view which shows the 3rd Example of this invention. The expanded sectional view after fluorescent substance filling which shows the 3rd Example of this invention. FIG. 2 is a schematic sectional view of a direct vapor deposition type phosphor of the present invention. The schematic sectional drawing of the indirect bonding type of the fluorescent substance of this invention. The schematic sectional drawing of the direct vapor deposition type of the fluorescent substance of a prior art example. The schematic sectional drawing of the indirect bonding type of the fluorescent substance of a prior art example. The expanded sectional view of the uneven | corrugated | grooved part of columnar shape fluorescent substance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor substrate 2 Photoelectric conversion part 3 Protective film 4 Phosphor 5 Convex part 6 Concave part 9 Phosphor substance 11 Support substrate

Claims (7)

In a phosphor plate comprising a phosphor layer having a surface on which a recess and / or a protrusion is formed,
A fluorescent plate, wherein the concave portion is filled with a fluorescent material.   The phosphor plate according to claim 1, wherein the phosphor layer contains cesium iodide (hereinafter referred to as CsI) as a main component.   The phosphor plate according to claim 1, wherein the phosphor layer has a columnar shape.   The fluorescent plate according to claim 1, wherein after the convex portion is removed, the concave portion is filled with the fluorescent substance.   The fluorescent plate according to claim 1 or 4, wherein the fluorescent substance is in a powder form.   The phosphor according to claim 1, 4, or 5, wherein the phosphor is mainly composed of CsI. 6. The fluorescent plate according to claim 1, wherein the fluorescent material contains gadolinium oxysulfide (hereinafter referred to as Gd ₂ O ₂ S) as a main component.

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